Localized Solar Collectors

a solar collector and localized technology, applied in the field of structures that promote localized heating, can solve the problems of high heat loss by convection, add complexity and cost to the solar energy harvesting system, and limit the application of low and medium temperature to small-scale residential and commercial us

Active Publication Date: 2017-02-09
MASSACHUSETTS INST OF TECH
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

Photo-thermal applications for harvesting solar energy currently suffer from low efficiency and require high concentrations of sunlight, which add complexity and cost to the solar energy harvesting systems.
Currently, low and medium temperature applications are limited to small-scale residential and commercial use.
However, the critical drawback of these systems is the high portion of heat loss by convection which is between 28-41% as measured by Otanicar et al., mentioned above.
This limitation puts a cap on further development of volumetric collectors.
Specifically, Au NPs in a microgel structure show enhanced temperatures with laser illumination and cause a collapse in the surrounding hydrogel matrix.
For plasmonic NPs, a comparison of the temperature rise calculated from the existing theories and the measured temperature rise from experiments generally does not show a good agreement between the theory and the experiments.
These methods, however, require high optical concentration and suffer from high optical loss and surface heat loss, or require vacuum to reduce convective heat loss under moderate optical concentration.
However, the solar-thermal conversion efficiency of the approach was still only 24%.
High optical concentrations limit the utilization of these approaches in stand-alone compact solar systems.
Furthermore, high optical concentrations add complexity and cost to the solar-thermal conversion system.

Method used

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Examples

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example 1

[0072]FIG. 8A shows the energy balance and heat transfer processes involved in a floating solar steam generator, including radiative and convective heat loss to the ambient and conductive and radiative heat loss to the underlying water, for a blackbody solar receiver operating at 100° C. The 1000 W / m2 delivered by the ambient solar flux is not enough to sustain the heat losses, and a 100° C. equilibrium temperature cannot be reached. FIG. 8B shows the energy balance and heat transfer processes in the heating structure shown in FIG. 8C according to embodiments of the present invention. FIG. 8C is a photograph of a heating structure 30 including a spectrally-selective solar absorber 34 having a spectrally-selective coating on a copper substrate to suppress radiative losses and to thermally concentrate heat to the evaporation region. The convective cover 36 includes a thermally insulating bubblewrap cover that transmits sunlight and minimizes convective losses. Slots were cut in the bu...

example 2

[0073]FIGS. 9A-9D show a lab-scale heating structure 30. Low-cost commercial materials were used to construct the heating structure 30, and even cheaper materials may be substituted for specific applications, e.g., using alternative selective coatings or replacing the copper film with an aluminum foil. The spectrally-selective solar absorber 34 was formed from a cermet (BlueTec eta plus) coated on a thermally-conductive copper substrate, as shown in FIGS. 9A and 9B. The spectrally-selective solar absorber 34 solar absorptance (α=0.93) and emittance at 100° C. (∈=0.07) were both measured. The thermal conductivity of copper is estimated to be 400 W / mK. The thermally insulating layer 32 was constructed from a polystyrene foam disk, as shown in FIGS. 9B and 9C, which is a thermal insulator (k=˜0.03 W / m-K) and serves to float the entire structure on a body of water, and limits the thermal conduction and radiation to the cool water underneath. A channel 38 was drilled through the foam, an...

example 3

[0074]To understand and quantify the dependence of evaporation heat transfer coefficient on the area of evaporation, the evaporation rate per area was experimentally measured for various evaporation layer 42 surface areas. These evaporation surfaces were created using a cotton fabric and shaped as circles with diameters from 4 mm to 24 mm. The evaporation heat transfer coefficient studies were carried out using small containers filled with water, such as shown in FIG. 10B. The evaporation layer 42 was formed from a cotton fabric that wicked the water to the surface to ensure good water-air contact for evaporation. The evaporation heat transfer coefficients were measured, and the results are shown in FIG. 10A. FIG. 10B shows the experimental set up for an evaporation layer 42 surface area of 24 mm. As shown in FIG. 10A, for smaller evaporation layer 42 areas, the evaporation heat transfer coefficient increases drastically, taking advantage of the better vapor diffusion geometries.

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Abstract

A localized heating structure includes a spectrally-selective solar absorber, that absorbs incident solar radiation and reflects at wavelengths longer than 2 μm, with an underlying heat-spreading layer having a thermal conductivity equal to or greater than 50 W / (mK), a thermally insulating layer, adjacent to the spectrally-selective solar absorber, having a thermal conductivity of less than 0.1 W / (mK), one or more evaporation openings through the spectrally-selective solar absorber and the thermally insulating layer, and an evaporation wick, disposed in one or more of the evaporation openings in the thermally insulating layer, that contacts liquid and allows the liquid to be transported from a location beneath the thermally insulating layer through to the spectrally-selective solar absorber in order to generate vapor from the liquid. The thermally insulating layer is configured to have a density less than the liquid so that the localized heating structure is able to float on the liquid.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This patent application claims the benefit of U.S. Provisional Patent Application No. 62 / 298,802 filed Feb. 23, 2016 and U.S. Provisional Patent Application No. 62 / 369,478 filed Aug. 1, 2016. This patent application is also a continuation-in-part of U.S. patent application Ser. No. 14 / 479,307 filed Sep. 6, 2014, now U.S. Pat. No. 9,459,024, which claims the benefit of U.S. Provisional Patent Application No. 61 / 874,390 filed Sep. 6, 2013. The disclosures of the above applications and patent are incorporated by reference herein in their entirety.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT[0002]This invention was made with Government support under Contract Nos. DE-SC0001299 and DE-FG02-09ER46577 awarded by the Department of Energy and under Contract No. FA9550-11-1-0174 awarded by the Air Force Office of Scientific Research. The Government has certain rights in the invention.TECHNICAL FIELD[0003]The present invention rela...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): F24J2/36F24J2/50F24J2/00
CPCF24J2/36F24J2002/508F24J2/506F24J2/0015B32B2266/06B32B5/18B32B5/32C08L83/02F22B1/006F24S10/17F24S10/80F24S70/10F24S80/525F24S80/56F24S80/65F24S90/00F24S2080/014Y02E10/44Y10T29/49826Y10T428/249967Y10T428/249969F24S20/25
Inventor NI, GEORGECHEN, GANGBORISKINA, SVETLANA V.COOPER, THOMAS ALAN
Owner MASSACHUSETTS INST OF TECH
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